James D. Santini, who served four terms in Congress as a Nevada Democrat, switched parties and battled Harry M. Reid unsuccessfully for a Senate seat in 1986, and became a travel industry lobbyist, died Sept. 22 at a hospice center in Rockville, Md. He was 78.

The cause was esophageal cancer, said a daughter, Lori Egbers. He was a resident of Potomac, Md.

A former justice of the peace and Nevada District Court judge, Mr. Santini was elected to the U.S. House of Representatives in 1974 and for years was the state’s only congressman.

In Washington, he focused less on national affairs than on matters of concern to Nevadans. He worked to promote tourism and chaired the House Interior and Insular Affairs mines and mining subcommittee.

Mr. Santini easily won reelection three times and, in 1982, challenged a powerful incumbent, Sen. Howard W. Cannon (D). Cannon was a senior member of the upper chamber but was vulnerable because of his association with a Teamsters union president who was being investigated for bribery.

Cannon denied wrongdoing, and he was never charged with a crime. But Mr. Santini benefited from the negative publicity and almost won the primary. Cannon lost in the general election to Republican Chic Hecht, a relatively obscure state senator.

Also in 1982, Mr. Santini’s congressional district was divided into two because of the state’s growing population. One district was won by Barbara F. Vucanovich, a Republican, and the other by Reid, a Democrat and a former Nevada Gaming Commission chairman.

Mr. Santini, who compiled a conservative record in the House, switched to the Republican Party in 1985. President Ronald Reagan had won a landslide reelection the year before, and Sen. Paul Laxalt (R), often called “Reagan’s best friend” in politics, was not seeking reelection in 1986.

Mr. Santini and Reid went after it.

Laxalt and Reagan backed Mr. Santini, but he lost in a bitterly contested race marked by negative ads and personal attacks, some of them focused on Mr. Santini’s conversion to the GOP.

“Democrats think of him as a turncoat, Republicans as an opportunist and independents tend to have a mix of these views,” one strategist told The Washington Post at the time. Reid went on to become Senate majority leader and is now the minority leader.

The 1986 race was Mr. Santini’s last attempt at public office. He spent much of his later career in Washington with the National Tour Association, retiring in 2010.

James David Santini was born in Reno, Nev., on Aug. 13, 1937. He graduated in 1959 from the University of Nevada at Reno and in 1962 from the University of California’s Hastings College of the Law in San Francisco.

After Army service from 1963 to 1966, he worked in Clark County, Nev., as a deputy district attorney, a public defender and a District Court judge.

Survivors include his wife of 47 years, Ann Crane Santini of Potomac; six children, David Santini of Reno, Lisa Boyd of Bethesda, Md., Katherine Santini of Benicia, Calif., Lori Egbers of Clifton, Va., Mark Santini of Potomac and J.D. Santini of Alexandria, Va.; and 13 grandchildren.